Interesting Mr. Lurker, I understand there is a third party site at which you can compare Amtrak fares for an array of dates - just like any airline offers at their own site. Whether that site is a travel agent at which the ticket can be booked, I know not (and really care not as I do not use any third party site for travel arrangements).
But I'm starting to lock things in for the existing itinerary, such as a Dinner with Atlanta friends and a hotel "down below".
Much as I would like to see the Chicago Symphony perform at Kravis Feb 26, the concert is completely sold, and I cannot be a "stage door Johnny", as I need to be back in the barn Feb 28. Hence I must be heading Northward Feb 26.
So the moral is, even if retired, there are still constraints when you do things duch as trips.